Squamous cell carcinomas are the most common cancer in the mucous membranes of the nose and throat. These account for about 3% of the cancers in the United States, resulting in about 30,5000 new cases per year.
The initial tumor is called the "primary." Primaries occur in various regions of the upper aerodigestive tract such as the tongue, tonsil, palate, etc.
Primary tumors have a tendency to spread (metastasize) to nearby lymph nodes. The lymph nodes trap the spreading tumor cells, but then the tumor starts to grow in these nodes and can then spread further. Lymph nodes of the head and neck occur in "clusters" named to indicate where the cluster is found, such as submental (below the chin), upper jugular (high in the anterior part of the neck), lower posterior cervical (low in the back of the neck), and so forth. Nodal clusters are similar on both sides of neck.
Lymph node clusters that contain tumor cells are called "positive." In relatively advanced cases, positive clusters can be detected by feeling a lump in the neck. These are termed clinical metastases because they are detected without pathologic confirmation. A problem with clinical data is that small positive nodes can be missed. Positive clusters can also be detected by a pathologist, who microscopically examines the nodes as they are removed during surgery.
A problem with pathological data about lymph nodes is that a node normally must be removed before it is known whether or not it is diseased. Further surgical treatment usually requires excision of both the primary tumor and any nodal clusters which have a high risk for metastases. Post-operative radiotherapy is sometimes used to kill any remaining malignant cells. The surgery, termed a neck dissection, may be of the radical type where all of the nodal clusters are removed, or of the selective type where only clusters thought to be positive are removed.
It is plainly desirable to detect and to remove all the positive nodes in order to prevent recurring tumors. It is likewise desirable to removed no more nodes than necessary in order to minimize the patient's post-operative morbidity. Any knowledge of consistent patterns in cervical metastases would thus be of value.
Unfortunately, although certain patterns in the spread of these tumors are recognized, these patterns are complicated. Tumors do not simply spread to the next physically nearest nodes. Nodes in close physical proximity to the primary may actually be less likely to be positive than more distant nodes. This can occur due to normal anatomic pathways which bypass adjacent nodal clusters. Complex patterns can also arise because the presence of tumor or previous treatment may cause aberrant pathways of lymphatic drainage by blocking normal channels.
The complexity is further increased because different primaries have different patterns of spread, even though the same nodal clusters are involved. For example, metastases can occur to both sides of the neck in some but not all cases as the primary approaches the midline.
Studies have been done which indicate the absolute frequency of occurrence of metastases for the various clusters of lymph nodes from each possible primary. These data are usually reported in multiple tables of positive nodes from different primaries. This traditional presentation is not in a form where complex patterns are readily apparent, however, head and neck surgeons, until now, have been forced to rely on their own experience when trying to determine which clusters the primary has metastasized during surgical excision of infected lymph nodes or during postoperative consultation with the patient.